COMPOSITION  OF  NORMAL  AND  MOTTLED 
CITRUS  LEAVES 


BY 

W.  P.  KELLEY  and  A.  B.  CUMMINS 


Reprinted  from  JOURNAL  OF  AGRICULTURAL  RESEARCH 

Vol.  XX,  No.  3 : : : Washington,  D.  C.,  November  1,  1920 


— ; 


PUBLISHED  BY  AUTHORITY  OF  THE  SECRETARY  OF  AGRICULTURE,  WITH 
THE  COOPERATION  OF  THE  ASSOCIATION  OF  LAND-GRANT  COLLEGES 


WASHINGTON : GOVERNMENT  PRINTING  OFFICE : 1920 


COMPOSITION  OF  NORMAL  AND  MOTTLED  CITRUS 

LEAVES1 


By  W.  P.  KEELEY  and  A.  B.  Cummins,  Citrus  Experiment  Station,  College  of 
Agriculture,  University  of  California 


INTRODUCTION 


Knowledge  concerning  the  composition  of  a plant  is  essential  to  an 
understanding  of  its  growth.  The  amounts  and  proportions  of  the 
different  constituents  absorbed  from  the  soil  or  other  nutrient  medium, 
as  revealed  by  accurate  analysis  of  the  several  parts  of  plants,  undoubt- 
edly give  some  indication  concerning  their  nutritional  requirements.  If 
determined  progressively,  such  data  may  contribute  to  a clearer  under- 
standing of  fundamental  physiological  processes  of  growth. 

The  interpretation  of  plant  analyses,  so  far  as  growth  processes  and 
requirements  are  concerned,  demands  great  caution,  however.  Many 
plants  undoubtedly  have  the  power  of  adapting  themselves  to  a wide 
range  of  soil  variations;  and  the  composition  of  the  plant,  owing  to 
selective  absorption,  commonly  bears  little  direct  relation  to  the  com- 
position of  the  nutrient  solution.  It  is  well  known  that  the  concentration 
of  a given  constituent  in  the  nutrient  solution  may  be  varied  considerably 
without  producing  any  material  change  in  the  composition  of  the  plant. 

The  effect  of  an  excess  or  deficiency  of  one  ion  on  the  absorption  of 
other  ions,  and  especially  the  effects  of  nonessential  salts  on  the  absorption 
of  essential  ions,  have  not  been  sufficiently  studied.  Despite  the  many 
investigations  during  recent  years  on  antagonism,  comparatively  few 
analyses  have  been  made  showing  the  effects  on  absorption.  Likewise, 
investigations  on  the  so-called  nutritional  or  physiological  diseases  have 
not  dealt  with  absorption  specifically,  except  to  a very  limited  extent. 

Previous  studies  on  the  rate  of  absorption  of  nutrients  have  been  con- 
ducted mainly  with  annual  plants,  chiefly  cereals,  very  limited  study 
having  been  devoted  to  trees.  There  is  much  need  for  accurate  data  on 
the  several  phases  of  absorption  as  related  to  the  growth  of  fruit  trees. 

1 Paper  No.  67,  University  of  California,  Graduate  School  of  Tropical  Agriculture  and  Citrus  Experiment 
Station,  Riverside,  Calif. 


(161) 


Journal  of  Agricultural  Research, 
Washington,  D.  C. 

vh 


Vol.  XX,  No.  3 
Nov.  1,  1920 
Key  No.  Calif .-34 


1 62  Journal  of  Agricultural  Research  vo1.xx,n0.3 

In  connection  with  investigations  on  the  nutrition  of  different  species 
of  citrus  trees,  especially  as  related  to  that  condition  known  as  mottle- 
leaf,  we  have  determined  the  composition  of  different  parts  of  the  tree, 
such,  for  example,  as  the  roots,  old  wood,  young  wood,  leaves,  leaf  sap, 
and  fruit.  This  work  has  extended  over  a period  of  several  years,  and 
further  study  is  contemplated.  Some  of  the  results  already  obtained 
have  proved  to  be  of  special  interest.  The  present  paper  will  be  devoted 
mainly  to  a discussion  of  the  composition  of  the  leaves. 

It  is  not  necessary  to  review  the  many  published  analyses  of  citrus 
fruits.  Most  of  the  publications  on  this  subject  have  dealt  mainly  with 
the  organic  constituents  and  total  ash,  with  an  occasional  analysis  of 
the  ash.  Comparatively  few  analyses  have  been  published  showing  the 
composition  of  portions  of  citrus  trees  other  than  the  fruit. 

The  earliest  investigation  we  have  been  able  to  find,  and  perhaps  the 
best  known,  is  that  of  Rowney  and  How  (15)  *,  published  in  1848.  Anal- 
yses were  reported  of  the  roots,  stems,  leaves,  and  fruit  of  orange  trees, 
Citrus  aurantium , grown  on  the  island  of  St.  Michael.  The  variety  was 
presumably  that  now  known  as  St.  Michael.1 2  The  analyses  were  ex- 
pressed as  percentages  of  the  carbon-dioxid-free  ash.  The  results  were 
similar  to  our  analyses  of  California  orange  trees,  when  calculated  to  the 
same  basis. 

In  1891  Oliveri  and  Guerrieri  (rj)  published  an  extended  study  on  the 
composition  of  the  wood,  leaves,  and  different  portions  of  the  fruit  of 
the  orange,  Citrus  aurantium  Riss;2  Mandarin,  C.  nobilis  var.  deliciosa, 
Swingle;  and  lemon,  C.  limonia  Osbeck,  grown  in  Palermo,  Italy.  This 
investigation,  extending  over  a period  of  three  years,  is  the  most  com- 
plete study  yet  published  on  the  composition  of  different  parts  of  citrus 
trees.  They  recorded  The  number  and  weights  of  fruits  produced  by 
different  classes  of  trees  and  the  number  and  weights  of  leaves  and  the 
weights  of  wood  pruned  from  the  trees  during  a period  of  three  years, 
representative  samples  of  which  were  analyzed.  Some  of  their  analyses 
also  agree  reasonably  closely  with  our  data. 

In  1901  Alino  ( 1 ) determined  the  phosphoric  acid,  potash,  and  nitrogen 
content  of  orange  wood,  leaves,  and  fruit;  and  in  1909  Muller  ( 12 ) pub- 
lished complete  analyses  of  seedling  orange  leaves  from  healthy  and 
diseased  trees  grown  in  South  Africa. 

In  1910  Blair  ( 2 ) analyzed  orange  leaves  and  stems  grown  in  Florida. 
His  samples  represented  the  new  growth  taken  in  October  from  certain 
plots  of  a fertilizer  experiment.  In  1917  Jensen  (7)  published  a paper 
on  the  composition  of  normal  and  mottled  orange,  lemon,  and  grape- 

1 Reference  is  made  by  number  (italic)  to  “ Literature  cited,”  p.  190-191. 

2 In  this  case,  the  sweet  orange,  Citrus  sinensis  Osbeck,  is  doubtless  the  species  studied.  W.  T. 
Swingle’s  revision  of  citrus  nomenclature,  as  given  in  the  “American  Standard  Cyclopedia  of  Horticulture,” 
is  followed  in  this  paper. 


Nov.  x,  1920  Composition  of  Normal  and  Mottled  Citrus  Leaves  163 


fruit  ( Citrus  grandis  Osbeck)  leaves  grown  in  California.  Further 
reference  will  be  made  to  this  paper  later. 

As  is  well  known,  the  composition  of  annual  herbaceous  plants  depends 
on  their  age.  It  has  been  shown  that  the  ash  content  and  the  proportions 
of  the  individual  constituents  absorbed  from  the  soil  change  as  growth 
proceeds.  Of  the  changes  in  perennials  much  less  is  known.  It  seems 
reasonable  to  suppose,  however,  that  the  growth  processes  are  similar. 
The  periodically  developing  new  shoots  may  be  likened  to  the  portion 
of  annual  plants  growing  above  ground. 

New  shoots  appear  on  citrus  trees  several  times  each  year.  The  tree, 
being  evergreen,  bears  leaves  at  all  seasons.  Consequently,  the  foliage 
is  composed  of  leaves  of  different  ages.  A given  leaf  ordinarily  remains 
on  the  tree  for  a period  of  from  two  to  three  or  more  years. 

SELECTION  OF  SAMPLES  * 

Special  care  has  been  taken  to  secure  representative  samples  of  leaves 
of  known  age.  Familiarity  with  the  appearance  of  developing  citrus 
leaves  proved  to  be  a material  aid  in  selecting  the  samples.  A consider- 
able portion  of  the  samples  were  obtained  from  trees  growing  near  the 
laboratory  where  daily  observations  were  made.  The  leaves  of  the 
Washington  Navel  and  Valencia  orange,  the  Eureka  lemon,  and  the 
Marsh  seedless  grapefruit  have  been  analyzed.  Each  sample  was  com- 
posed of  several  hundred  leaves,  collected  from  six  or  more  adjacent 
trees,  all  of  which  were  reasonably  uniform  in  appearance  and  the  culture 
and  fertilization  of  which  had  been  the  same.  The  trees  were  10  or  more 
years  of  age.  The  entire  leaf,  including  the  petiole,  was  analyzed  as  a unit. 

The  samples  were  picked  from  the  trees,  placed  in  tight  bags  and 
immediately  taken  to  the  laboratory  and  weighed.  In  most  cases  this 
procedure  did  not  require  more  than  30  minutes.  In  order  to  remove 
dust  and  other  adhering  foreign  material,  the  leaves  were  thoroughly 
cleaned  by  wiping  each  leaf  with  a moist  cloth,  but  washing  with  water 
was  necessary  with  a few  samples  heavily  coated  with  dust  or  showing 
evidences  of  residues  from  previous  spraying.  Early  in  this  work  it  was 
found  that  the  samples  from  which  the  dust  had  not  been  completely 
removed  contained  abnormally  high  percentages  of  silica,  alumina,  iron, 
and  inorganic  materials  not  soluble  in  dilute  hydrochloric  acid. 

METHODS  OF  ANALYSIS 

The  samples  were  dried  at  105°  C.  for  24  hours,  and  the  loss  in  weight 
was  calculated  as  moisture.  The  dry  samples  were  ground  to  a powder  in 
a small  hand  mill,  were  thoroughly  mixed,  and  were  then  stored  in 
tightly  stoppered  bottles  for  analysis. 

Total  nitrogen  was  determined  by  the  official  Kjeldahl  method,  modified 
to  include  nitrates.  Total  sulphur  was  determined  by  the  sodium-peroxid 


164 


Journal  of  Agricultural  Research 


Vol.XX,No.3 


fusion  method.  The  fusions  were  made  over  alcohol  flames,  and  the 
sulphate  was  precipitated  as  barium  sulphate,  usually  from  the  solution 
of  the  entire  mass  used  in  making  the  fusion.  Total  phosphorus  was 
determined  by  treating  1 to  2 gm.  of  the  dry  material  with  a solution  of 
magnesium  nitrate,  evaporating  to  dryness,  igniting,  and  proceeding 
in  the  usual  manner.  Chlorin  was  determined  in  a special  portion  of  the 
ash  made  by  igniting  at  a low  heat  5 to  10  gm.  of  the  dry  material,  dis- 
solving the  residue  in  dilute  nitric  acid,  and  proceeding  with  the  Volhard 
volumetric  method.  In  some  cases  chlorin  was  also  determined  by  per- 
forming the  incineration  in  the  presence  of  an  excess  of  sodium  carbonate 
in  order  to  avoid  the  possible  loss  of  chlorin,  but  the  results  of  the  two 
methods  were  similar. 

For  the  determination  of  total  ash,  10  to  20  gm.  of  the  dry  samples 
were  incinerated  in  porcelain  dishes  over  Bunsen  burners.  The  material 
charred  easily  and  burned  quietly  upon  the  application  of  low  heat  and 
was  reduced  to  a gray  ash  without  approaching  dull  redness.  The 
residue  was  then  allowed  to  cool,  was  taken  up  with  hot  water,  trans- 
ferred to  a filter,  and  washed  thoroughly.  The  insoluble  material  with 
its  filter  paper  was  transferred  to  a platinum  dish,  dried,  pulverized 
with  an  agate  pestle,  and  heated  to  full  redness.  When  the  platinum 
dish  cooled,  the  filtrate  from  the  previous  leaching  was  added  and 
evaporated  to  dryness.  Ten  to  20  cc.  of  strong  ammonium-carbonate 
solution  were  then  added,  and  the  treatment  was  repeated  until  the 
ash  was  completely  carbonated,  as  was  indicated  by  constant  weight 
upon  evaporating  to  dryness  and  heating  gently.  The  results  are  re- 
corded as  percentages  of  ash.  It  should  be  stated  that  the  ash  thus 
obtained  differs  from  that  reported  by  other  investigators  in  that  we  are 
dealing  with  completely  carbonated  ash,  whereas  previous  analyses  of 
citrus  leaf  ash  have  been  calculated  to  a carbon-dioxid-free  basis. 

The  ash  was  dissolved  in  water  and  dilute  hydrochloric  acid,  and  the 
solution  was  evaporated  to  complete  dryness  on  the  water  bath  in  order 
to  dehydrate  the  silica.  The  amount  of  uncombined  carbon  found  in 
the  ash  was  always  entirely  negligible.  The  residue  was  taken  up  with 
warm  water  and  dilute  hydrochloric  acid.  The  silica  was  determined 
by  the  loss  in  weight  occasioned  by  treating  the  incinerated  residue  with 
hydrofluoric  acid.  The  material  nonvolatile  in  hydrofluoric  acid  usually 
amounted  to  only  0.1  to  0.2  per  cent  of  the  ash  and  was  neglected  in 
this  work.  The  filtrate  from  the  silica  separation  was  made  up  to  a 
definite  volume,  usually  500  cc.,  and  the  various  constituents  were 
determined  in  aliquots  representing  from  0.2  gm.  to  0.4  gm.  of  the  ash. 

The  methods  of  the  Association  of  Official  Agricultural  Chemists  1 
were  used  with  slight  modifications,  as  noted.  Iron,  aluminum,  and 

1 Wiley,  H.  W.,  ed.  official  and  provisional  methods  of  analysis,  association  of  official  agri- 
tural  chemists.  As  compiled  by  the  committee  on  revision  of  methods.  U.  S.  Dept.  Agr.  Bur.  Chem. 
Bui.  107  (rev.),  272  p.,  13  fig.,  1908.  Reprinted  in  1912. 


Nov.  i,  1920 


Composition  of  Normal  and  Mottled  Citrus  Leaves  165 


phosphoric  acid  were  precipitated  collectively  by  adding  a weighed 
excess  of  ferric  chlorid,  neutralizing  with  ammonia,  filtering,  redissolving 
in  dilute  hydrochloric  acid,  and  repeating  the  process.  Iron  was  pre- 
cipitated with  ammonia  from  a separate  aliquot  and  determined  volu- 
metrically  by  reduction  with  zinc  and  titration  with  permanganate. 
This  method  was  occasionally  supplemented  by  the  ferrocyanid  colori- 
metric method  with  fairly  satisfactory  results.  Aluminum  was  calculated 
by  difference  after  the  phosphoric  acid  was  gravimetrically  determined 
in  a separate  aliquot.  Calcium,  magnesium,  potassium,  and  sodium  were 
determined  in  the  filtrate  after  the  ammonia  precipitate  was  removed, 
and  in  some  cases  manganese  was  determined  by  bromin  oxidation. 
Sulphate  was  determined  gravimetrically  in  an  aliquot  of  the  original 
solution.  Carbon  dioxid  was  not  determined. 

COMPOSITION  OF  NORMAL  MATURE  ORANGE  LEAVES 

A considerable  number  of  analyses  have  been  made  of  mature  orange 
leaves  representing  both  the  Washington  Navel  and  Valencia  varieties. 
Owing  to  the  absence  of  previous  records  showing  the  age  of  the  leaves 
available  for  analysis,  and  in  view  of  the  fact  that  orange  leaves,  when 
from  4 to  6 months  of  age,  assume  an  appearance  not  unlike  that  of 
leaves  1,  2,  or  more  years  of  age,  it  is  highly  probable  that  random  sam- 
ples will  always  represent  mixed  ages.1  Most  of  our  samples  of  mature 
leaves  were  taken  at  random,  always  avoiding  immature  or  abnormal 
individuals.  The  samples  were  gathered  at  different^  seasons  of  the 
year  and  from  a considerable  number  of  different  sets  of  trees,  some  of 
which  were  growing  in  different  localities.  Typical  analyses  are  sub- 
mitted in  Tables  I and  II. 

It  is  interesting  to  note  that  the  composition  of  the  different  samples 
was  found  to  be  reasonably  uniform  despite  the  fact  that  their  averageages, 
although  they  were  mature  in  appearance,  probably  varied  considerably. 
Other  samples  not  reported  above  showed  a similar  composition.  The  data 
also  afford  but  little  evidence  of  seasonal  variation  in  composition. 

Except  in  calcium  and  potassium  content,  the  different  samples  of 
the  same  variety  differed  almost  as  widely  in  composition  as  the  samples 
of  different  varieties.  The  samples  from  different  localities  were  also 
similar  in  composition,  although  those  from  Riverside  were  grown  on 
sandy  loam  soil,  that  from  Anaheim  on  light  sandy  soil,  and  the  one  from 
Whittier  on  heavy  adobe. 

It  will  be  noted  that  the  average  calcium  content  of  Valencia  leaves 
was  found  to  be  somewhat  higher  than  that  of  Navels,  while  the  reverse 
is  true  for  potassium. 

‘Ensign  (6)  has  recently  shown  that  the  size  of  the  vein  islets  of  Citrus  grandis  is  directly  correlated  with 
the  maturity  of  the  leaf.  Erom  the  most  immature  to  fully  matured  leaves  there  is  a gradual  increase  in 
the  size  of  the  vein  islets.  If  further  investigation  prove  that  similar  relations  occur  in  other  species  of 
citrus,  a direct  means  will  be  afforded  by  which  the  age  of  the  leaves  can  be  determined. 


Table  I. — Composition  of  mature  normal  orange  leaves 

NAVEL 


166 


Journal  of  Agricultural  Research 


Vol.XX,  No.  3 


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Nov.  i,  1920 


Composition  of  Normal  and  Mottled  Citrus  Leaves  167 


Throughout  this  work  we  have  determined  the  aluminum.  Quali- 
tative tests  usually  indicated  this  element  to  be  present,  but  the  quantity 
was  never  more  than  a few  tenths  of  1 per  cent  of  the  ash.  Frequently 
the  amount  was  undeterminable.  The  manganese  was  also  determined  in 
several  samples.  The  amount  was  found  to  vary  from  0.1  per  cent  to 
0.2  per  cent  of  the  ash. 

The  size  of  the  leaves  as  gauged  by  their  average  weights  was  recorded, 
but  there  appears  to  be  no  consistent  difference  in  composition  referable 
to  the  size  of  the  leaf.  As  is  well  known,  the  size  of  apparently  normal 
orange  leaves  may  vary  widely.  Even  on  a given  tree,  the  fully  mature 
leaves  of  certain  cycles  of  growth  may  be  at  least  twice  as  large  as  others. 

From  the  analysis  of  many  other  samples  in  this  laboratory  it  may  be 
said  that  the  composition  of  mature  orange  leaves  when  grown  in  Cali- 
fornia is  remarkably  uniform,  provided,  however,  that  the  leaves  be 
borne  on  vigorous  trees.  On  the  other  hand,  the  composition  of  the  leaves 
of  improperly  nourished  and  diseased  trees  may  vary  widely.  If  the 
supply  of  available  nitrate  be  deficient,  the  content  of  nitrogen  in  the 
leaves  may  be  considerably  below  that  reported  above,  but  there  seems 
to  be  some  doubt  whether  the  reverse  is  true. 

COMPOSITION  OF  LEMON  AND  GRAPEFRUIT  LEAVES 

The  analysis  of  mature  Eureka  lemon  and  Marsh  seedless  grapefruit 
leaves  is  submitted  in  Tables  TTI  and  IV. 

Two  of  the  samples  of  lemon  leaves  were  collected  in  midwinter  and 
the  other  on  August  29.  They  were  grown  on  widely  different  types 
of  soil.  The  Riverside  sample  grew  on  sandy  loam,  the  Whittier  sample 
on  heavy  adobe,  and  the  Tustin  sample  on  highly  calcareous  sandy  loam 
soil.  The  grapefruit  leaves  were  grown  on  sandy  loam. 

The  composition  of  the  different  samples  of  lemon  leaves  is  fairly 
uniform,  the  average  being  similar  to  the  average  composition  of  Valencia 
orange  leaves.  On  the  other  hand,  the  composition  of  the  grapefruit 
leaves  closely  resembles  that  of  Navel  orange  leaves. 

The  composition  of  the  leaves  of  the  different  varieties  and  species  of 
citrus  has  been  found  to  be  remarkably  uniform  from  the  standpoint  of 
both  the  ash  and  the  dry  matter.  A more  detailed  discussion  of  the 
composition  will  be  given  below. 


Table  III.— Composition  of  mature  lemon  and  grapefruit  leaves 

LEMON 


Journal  of  Agricultural  Research 


Vol.  XX,  No.  3 


1 68 


Riverside Dec.  10,1917  I 59.39  17-65  0.38  0.016  5- Si  0.41  1.06  0.04 


Nov.  1. 1920  Composition  of  Normal  and  Mottled  Citrus  Leaves  169 


COMPOSITION  OF  ORANGE  LEAVES  AT  DIFFERENT  STAGES  OF  GROWTH 

The  results  obtained  from  the  analysis  of  samples  of  leaves  approxi- 
mately one  month  of  age,  gathered  on  May  11,  1917,  were  found  to  be 
considerably  different  from  previous  analyses  of  mature  leaves.  Samples 
representing  the  new  spring  growth  and  that  of  the  previous  year,  gathered 
from  the  same  trees  on  May  21,  1917,  also  proved  to  be  widely  different 
in  composition.  These  results,  together  with  the  discordance  between 
the  analyses  previously  made  in  this  laboratory  and  those  published  by 
Blair  ( 2 ) from  Florida  and  by  Jensen  (7)  from  California,  suggested  the 
desirability  of  making  a study  on  the  composition  of  orange  leaves  at 
different  stages  of  growth. 

Samples  were  collected  at  four  different  intervals  in  the  growth  cycle. 
The  first  represented  leaves  approximately  1 week  old ; the  second,  those 
6 to  8 weeks  old;  the  third,  leaves  at  full  maturity,  the  ages  of  which 
ranged  from  6 months  to  approximately  2 years;  the  fourth,  old  leaves 
that  were  about  to  be  shed,  as  indicated  by  their  yellowish  brown  color. 
Each  sample  was  picked  from  six  normal,  vigorously  growing  trees  of 
plot  V at  the  Citrus  Experiment  Station,  Riverside,  Calif.  The  samples 
representing  different  ages  were  all  taken  from  the  same  trees,  and  those 
representing  the  first  three  periods  of  growth  were  gathered  on  the  same 
day,  November  9,  1917.  These  trees  support  an  abundant  foliage;  and, 
as  frequently  occurs,  they  at  that  time  bore  numerous  shoots  of  varying 
ages,  ranging  from  a few  days  to  2 or  more  years  of  age,  which  made  it 
possible  to  secure  samples  of  widely  different  ages  on  a given  day.  The 
samples  of  old  leaves  were  gathered  December  10,  1917. 

The  data  expressed  as  percentages  of  the  ash  show  that  notable 
changes  take  place  in  the  relations  of  certain  constituents  as  growth 
proceeds.  Especially  prominent  among  these  changes  are  the  decreases 
in  the  percentages  of  phosphate  and  potassium,  on  the  one  hand,  and  the 
increases  in  calcium  on  the  other.  For  example,  the  ash  of  navel 
leaves  at  the  age  of  1 week  was  found  to  contain  16.83  Per  cent  phosphate 
(P04),  at  6 weeks  7.10  per  cent,  at  maturity  2.47  per  cent,  while  the  ash  of 
old  leaves  contained  only  1.32  per  cent. 

The.  changes  in  the  percentages  of  potassium  were  quite  parallel  to 
those  of  phosphate.  When  navel  leaves  were  1 week  of  age,  the  ash 
contained  19.87  per  cent  potassium,  when  6 weeks  of  age,  10.32  per  cent, 
when  .mature,  5.68  per  cent,  while  the  old  leaves  contained  only  1.66 
per  cent. 

The  percentages  of  calcium  underwent  changes  quite  opposite  to  those 
of  potassium.  With  the  ash  containing  20.72  per  cent  calcium  when 
the  leaves  were  1 week  old  there  was  an  increase  to  28.44  Per  cent 
at  6 weeks,  to  33.21  per  cent  at  maturity,  and  finally  to  34.41  per  cent 
in  the  very  old  stage. 


170 


Journal  of  Agricultural  Research 


Vol.  XX,  No.j 


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Composition  of  Normal  and  Mottled  Citrus  Leaves 


171 


Among  the  other  necessary  nutrients,  the  percentages  of  iron,  magne- 
• sium,  and  sulphate  decreased  with  age,  although  to  a lesser  degree  than 
potassium  and  phosphate.  The  ash  of  the  youngest  leaves  contained 
approximately  twice  as  much  iron  as  that  of  the  mature  leaves,  ancl 
differences  almost  as  great  occurred  in  the  percentages  of  magnesium 
and  sulphate. 

As  was  anticipated,  the  changes  that  take  place  in  Valencia  orange 
leaves  are  quite  similar  to  those  of  navel  leaves. 

The  percentages  of  phosphorus  and  sulphur  refer  to  the  total  amounts 
as  determined  by  the  magnesium-nitrate  and  sodium-peroxid  fusion 
methods,  respectively,  and  are  somewhat  higher  than  the  corresponding 
data  calculated  from  the  ash  analyses.  As  is  well  known,  organic 
materials  usually  lose  a portion  of  their  phosphorus  and  sulphur  in  the 
ashing  process. 

It  will  be  noted  that  the  content  of  water  decreased  considerably  as 
growth  took  place.  At  1 week  of  age  the  navel  leaves  contained  72.31 
per  cent  water,  at  6 weeks  70.81  per  cent,  at  maturity  60.98  per  cent, 
and  the  very  old  leaves  still  contained  60.73  per  cent.  The  content  of 
total  ash,  on  the  other  hand,  increased  markedly  with  age,  rising  from 
6.54  per  cent  of  the  dry  matter  at  the  age  of  1 week  to  the  very  high 
content  of  21.39  per  cent  in  the  old  leaves. 

The  nitrogen  decreased  from  3.01  per  cent  at  the  age  of  1 week  to  2.39 
per  cent  at  maturity,  and  finally  to  1.31  per  cent  in  the  old  stage.  The 
percentage  of  phosphorus  decreased  still  more  rapidly  during  the  actively 
growing  period,  but  later  the  phosphorus  content  remained  approxi- 
mately constant.  The  percentage  of  potassium  also  decreased  rapidly 
during  the  early  period  of  growth  but  remained  almost  constant  after 
the  second  period  until  the  period  of  senility  approached,  when  a still 
further  decrease  took  place. 

The  percentage  of  iron  in  the  dry  matter  was  found  to  be  reasonably 
constant  at  all  stages  of  growth.  However,  in  considering  the  iron  con- 
tent of  these  and  all  other  samples  reported  herein,  it  is  important  to 
bear  in  mind  that  the  analytical  error  involved  in  the  determination  of 
small  amounts  of  this  element  is  likely  to  be  relatively  great.  For  this 
reason  small  variations  in  the  results  are  probably  not  significant. 
The  percentages  of  sulphur  and  magnesium  each  increased  somewhat 
as  growth  took  place. 

The  constituent  of  the  dry  matter  of  orange  leaves  that  undergoes  the 
greatest  percentage  change  as  a result  of  growth  is  calcium.  At  1 week 
of  age,  the  navel  leaves  contained  1.3*6  per  cent  calcium,  at  6 weeks 
2.62  per  cent,  at  maturity  5.63  per  cent,  and  the  very  old  leaves  contained 
7.36  per  cent. 

Of  the  supposedly  unessential  constituents,  the  greatest  concentration 
of  sodium  was  found  in  the  young  leaves;  but  the  amount  was  always 
small,  while  the  data  for  silica  and  chlorin  show  no  consistent  variation. 


172 


Journal  of  Agricultural  Research 


Vol.XX,No.3 


It  is  interesting  to  note  that  in  certain  respects  the  composition  of 
orange  leaves  changes  with  growth,  somewhat  as  is  the  case  with  the  • 
vegetative  portion  of  other  plants.  With  certain  cereals  a considerable 
portion  of  the  potassium,  magnesium,  phosphorus,  and  nitrogen  migrate 
from  the  leaves  into  other  parts  of  the  plant  as  maturity  approaches  (9, 
jo).  The  potassium  tends  to  accumulate  in  the  straw  of  rice,  while  the 
magnesium,  phosphorus,  and  nitrogen  are  translocated  to  the  grain. 

The  composition  of  citrus  leaves  differs  markedly  from  that  of  cereals 
in  certain  other  respects.  The  ash  content  of  the  former  increases  much 
more  rapidly  and  reaches  a very  high  point  in  the  old  leaves.  The  cal- 
cium content  increases  very  rapidly  during  the  most  actively  growing 
period  and  continues  to  be  deposited  in  the  leaves,  although  at  a some- 
what slower  rate,  almost  until  the  time  the  leaves  fall  off. 

While  it  is  probable  that  the  composition  of  normal  orange  leaves 
varies  to  some  extent  when  grown  in  different  parts  of  the  world  or  on 
different  soils  in  a given  locality,  careful  study  of  the  analyses  of  the 
Florida-grown  leaves  published  by  Blair  (2)  and  those  reported  from 
Italy  by  Olivieri  and  Guerrieri  ( 1 3)  suggests  that  these  were  immature 
leaves.  From  Jensen’s  results  (7),  it  is  evident  that  his  samples  were 
not  composed  of  mature  leaves.  Recognition  of  the  relationships  be- 
tween the  age  and  the  composition  of  orange  leaves  is  especially  im- 
portant in  the  study  of  the  composition  of  mottled  leaves,  as  will  be 
pointed  out  more  fully  later. 

It  does  not  necessarily  follow  from  the  preceding  discussion  that  a por- 
tion of  a given  element,  potassium,  for  example,  migrates  back  into  other 
parts  of  the  tree  after  the  leaves  reach  a certain  stage  of  development. 
Increase  in  the  size  of  a leaf,  owing  to  the  elaboration  of  carbonaceous 
matter,  may  dilute  the  nutrients  present  and,  therefore,  lower  the  per- 
centage without  there  being  an  actual  loss.  To  establish  this  point,  it  is 
necessary  to  determine  the  weights  of  the  constituents  present  per  leaf  at 
different  periods.  From  the  average  weights  of  the  individual  leaves  at 
each  period  we  have  calculated  the  content  of  the  different  constitu- 
ents, expressing  the  results  in  grams  per  1,000  leaves.  (Table  VII.) 

The  old  Navel  leaves  were  considerably  smaller  on  the  average  than 
either  those  representing  maturity  or  6 weeks  of  age,  while  the  mature 
Valencia  leaves  were  larger  than  the  old  leaves  of  the  same  variety.  In 
addition,  the  leaves  of  each  sample  of  the  Valencia  variety  were  consider- 
ably larger  than  the  corresponding  Navel  leaves. 

Despite  these  irregularities  in  the  size  of  the  leaves,  the  data  show  that 
the  content  of  calcium  in  a given- orange  leaf  increases  very  rapidly  during 
the  early  part  of  the  growth  period.  In  the  Navel  leaves,  approximately 
a tenfold  increase  in  calcium  content  took  place  between  the  first  and  the 
sixth  week  of  age.  From  the  sixth  week  to  maturity  a further  increase, 
more  than  twofold,  took  place,  and  finally  the  calcium  content  increased 
still  further  as  the  leaves  approached  the  time  of  normal  dropping. 


Not.  x,  1920  Composition  of  Normal  and  Mottled  Citrus  Leaves  1 73 


• </) 

MM  H O 

v 5 w 
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174 


Journal  of  Agricultural  Research 


Vol.XX,  No.  3 


The  rates  of  increase  in  magnesium  and  sulphur  are  also  rapid  during 
the  early  part  of  the  growth  period,  and  each  of  these  constituents  con- 
tinues to  accumulate  in  the  leaves  up  to  maturity,  but  the  absolute 
amounts  never  become  high.  Since  irregularities  occurred  in  the  size 
of  the  leaves,  it  is  doubtful  whether  any  important  amount  of  either 
magnesium  or  sulphur  is  translocated  to  other  portions  of  the  tree  after 
maturity  has  been  reached. 

The  maximum  amounts  of  potassium,  phosphorus,  and  nitrogen  were 
deposited  before  the  leaves  were  6 weeks  of  age.  The  rates  of  increase 
of  each  were  considerably  less  than  that  of  calcium.  The  data  show  that 
a considerable  portion  of  these  elements  migrates  away  from  the  leaves 
after  certain  periods.  With  potassium  and  nitrogen  the  loss  takes  place 
after  maturity  has  been  reached,  while  the  phosphorus  begins  to  recede 
even  before  maturity  is  attained. 

Similar  data  for  iron  are  omitted  because  of  the  magnitude  of  the  ana- 
lytical error  involved  in  its  determination. 

Samples  representing  more  frequent  intervals  in  the  growth  cycle 
would  certainly  afford  more  detailed  information  regarding  absorp- 
tion. It  is  possible  that  the  analysis  of  such  samples  when  plotted 
might  show  breaks  in  the  curves  not  indicated  by  the  existing  data. 
For  example,  the  exact  period  in  the  growth  cycle  when  the  leaves  con- 
tained the  maximum  amount  of  potassium  might  be  shifted  to  some 
extent  and  other  fluctuations  might  also  be  found.  However,  other 
analyses  of  immature  orange  leaves  at  different  seasons  of  the  year  show 
a fairly  close  agreement  with  those  reported  above.  On  the  whole,  we 
are  inclined  to  believe  that  the  main  features  of  the  composition  of  the 
orange  leaf  have  been  determined. 

It  seems  appropriate  to  emphasize  the  fact  that  citrus  leaves  are  ex- 
tremely calcareous,  and  much  more  so  than  most  of  the  economic  plants. 
As  is  well  known,  the  ash  of  some  of  the  legumes  contains  high  percentages 
of  calcium,  but  relatively  few  have  been  reported  to  contain  as  high  per- 
centages of  calcium  as  citrus  leaves.  Not  only  is  the  ash  of  citrus  leaves 
high  in  calcium  but  the  total  ash  content  is  high  also.  It  is  unusual  to 
find  dried  plant  material  that  contains  from  5 to  7 per  cent  calcium. 

COMPOSITION  OF  MOTTLED  ORANGE  LEAVES 

The  condition  of  citrus  trees  known  as  mottle-leaf  has  been  widely' 
discussed.  Much  study  has  already  been  devoted  to  it,  and  several 
hypotheses  have  been  advanced  concerning  the  disease.  The  symptoms, 
mode  of  occurrence,  and  general  distribution  were  fully  discussed  in  a 
paper  by  Briggs,  Jensen,  and  McLane  (3).,  The  disease  is  commonly 
thought  to  result  from  some  nutritional  disturbance,  but  the  cause  has 
not  been  definitely  determined. 


Table  VIII. — Composition  of  mottled  orange  leaves 

NAVEL 


Nov.  i,  1920 


Composition  of  Normal  and  Mottled  Citrus  Leaves  175 


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Riverside,  plot  A June  13,  1916  62.16  13.94  0.57  3-87  0.33  1.42  0.13  0.17  0.38  2.59 

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176 


Journal  of  Agricultural  Research 


Vo1.XX,No.3 


We  have  analyzed  different  portions  of  orange  and  lemon  trees  affected 
with  mottle-leaf,  as  well  as  grapefruit  leaves  and  samples  representing 
different  degrees  of  mottling.  Most  of  the  samples  were  collected  from 
the  fertilizer  plots  of  the  Citrus  Experiment  Station.  In  all  cases  the 
leaves  were  collected  from  shoots  6 or  more  months  of  age.  The  analysis 
of  orange  leaves  in  an  advanced  stage  of  mottling  is  presented  in  Tables 
VIII  and  IX. 

Comparison  of  the  data  with  the  previously  submitted  analyses  shows 
at  once  that  the  composition  of  mottled  leaves  differs  considerably 
from  that  of  average  mature  normal  leaves.  The  principal  differences 
are  found  in  the  greater  percentages  of  potassium  and  phosphate,  on 
the  one  hand,  and  the  lesser  percentages  of  calcium  on  the  other.  The 
ash  of  mottled  leaves  also  contains  greater  percentages  of  magnesium 
and  sulphate,  while  the  iron,  silica,  sodium,  and  chlorin  do  not  differ 
materially. 

Considerable  variations  will  also  be  noted  among  the  different  samples 
of  mottled  leaves.  This  is  probably  due  to  the  varying  degrees  of 
mottling  represented  by  the  samples.  However,  every  sample  of 
mottled  leaves  that  has  been  analyzed  in  this  laboratory  has  been  found 
to  vary  from  the  normal  in  the  same  general  direction. 

The  average  content  of  water  in  mottled  leaves  was  found  to  be 
slightly  higher  than  in  normal  leaves  and  the  ash  content  somewhat 
lower.  Considering  the  dry  matter,  the  most  pronounced  differences 
are  found  in  the  lesser  calcium  content,  on  the  one  hand,  and  the  abnor- 
mally high  percentages  of  potassium  and  phosphorus  in  mottled  leaves, 
on  the  other.  The  average  nitrogen  content  of  mottled  leaves  is  also 
considerably  above  normal,  as  was  previously  pointed  out  by  McBeth  (u). 

From  his  analyses  of  normal  and  mottled  citrus  leaves,  Jensen  (7) 
failed  to  find  any  consistent  difference  in  composition.  In  order  to 
insure  uniformity  in  the  age  of  his  samples,  he  collected  the  leaves  from 
the  current  season’s  growth.  On  the  dates  two  of  his  samples  were 
collected,  April  18  and  May  11,  the  current  season’s  growth  is  probably 
never  mature  at  Riverside.  Furthermore,  the  calcium  content,  which 
he  reported,  was  very  much  below  that  of  any  mature  normal  orange 
leaf  we  have  been  able  to  find.  It  seems  safe  to  conclude,  therefore,  that 
Jensen’s  studies  were  made  with  immature  leaves.  It  is  possible,  of 
course,  that  the  variations  in  composition  incident  to  mottling  may 
not  occur  until  after  the  leaves  have  reached  a certain  stage  of  growth, 
although  recent  analysis  of  a sample  of  leaves  about  10  days  of  age, 
taken  from  severely  mottled  trees,  indicates  that  the  composition  may 
begin  to  diverge  from  the  normal  at  a very  early  period. 

It  is  well  known  that,  with  the  exception  of  severe  cases  of  mottle-leaf, 
the  discoloration  ordinarily  does  not  become  apparent  until  the  leaves 
have  reached  an  age  of  2 to  3 months.  Subsequently,  the  degree  of 
discoloration  becomes  increasingly  intense  until  the  period  of  normal 


Nov.  i,  i92o  Composition  of  Normal  and  Mottled  Citrus  Leaves  177 


maturity.  In  addition,  mottle-leaf  is  usually  most  pronounced  from 
September  to  February,  when  it  becomes  very  noticeable  on  the  leaves 
of  the  previous  spring  and  summer  cycles  of  growth.1 

Some  light  may  be  thrown  on  mottle-leaf  by  comparing  the  compo- 
sition of  mottled  leaves  with  that  of  normal  leaves  at  different  stages 
of  growth.  By  reference  to  Tables  V and  VIII  it  will  be  seen  that  the 
composition  of  the  ash  of  the  former  is  quite  similar  to  that  of  normal 
leaves  approximately  6 weeks  of  age,  although  the  total  ash  content  of 
mottled  leaves  is  considerably  higher  (compare  Tables  VI  and  IX). 
It  is  especially  interesting  to  note  that  the  nitrogen  content  of  mottled 
leaves  is  somewhat  higher  than  that  of  normal  leaves  at  the  age  of  1 
week  and  much  greater  than  that  of  normal  leaves  at  the  age  of  6 weeks. 

The  data  indicate,  therefore,  that  the  essential  nutrients  are  depos- 
ited in  mottled  orange  leaves  at  abnormal  rates.  A satisfactory  expla- 
nation of  this  fact  can  not  now  be  given.  The  rising  sap  is  itself  probably 
abnormal  in  composition. 

By  calculating ' the  weights  of  the  several  constituents  contained  in 
a unit  number  of  mottled  leaves,  it  is  found  (Table  X)  that  notwith- 
standing the  fact  that  the  average  size  of  the  mottled  leaves  was  less 
than  one-half  that  of  normal  leaves  they  contained  as  great  amounts  of 
potassium  and  approximately  as  much  phosphorus  per  leaf  (compare 
Tables  VII  and  X).  On  the  other  hand,  the  content  of  calcium  was 
less  than  one- third  as  great  as  normally  occurs,  while  the  magnesium, 
sulphur,  and  nitrogen  were  intermediate  in  amount.2 

The  preceding  analyses  represent  extreme  cases  of  mottling.  Sam- 
ples of  Valencia  orange  leaves  at  a less  advanced  stage  have  also  been 
studied.  These  latter  were  of  an  intermediate  size,  showing  the  typical 
yellowish  spots  between  the  veins.  They  were  selected  from  trees  a 
considerable  portion  of  whose  foliage  was  normal  and  some  of  which 
bore  a fair  crop  of  fruit.  The  results  are  recorded  in  Table  XI 

The  percentages  of  calcium  and  potassium  closely  approach  those  of 
severely  mottled  Valencia  leaves  (Tables  VIII  and  IX),  but  the  phos- 
phorus content  is  more  nearly  normal.  The  percentage  of  nitrogen  was 
found  to  be  no  greater  than  occurs  in  normal  Valencia  leaves. 

Thus,  it  appears  that  the  early  stages  of  mottling  are  first  attended  by 
the  absorption  of  subnormal  amounts  of  calcium  3 and  supernormal 
amounts  of  potassium  and  phosphorus,  and  that  modifications  in  the 
absorption  of  nitrogen  occur  later. 

1Mottled  leaves  fall  off  in  large  numbers  during  the  latter  part  of  the  winter  and  early  spring.  New 
shoots  developing  at  this  season  give  the  trees  the  appearance  of  having  recovered  from  the  disease.  These 
latter,  however,  may  become  mottled  the  following  fall.  It  is  never  safe  to  pass  judgment  on  the  state 
of  the  disease  in  the  spring  or  early  summer.  We  have  never  known  of  a leaf  once  severely  mottled  which 
became  normal  later.  New  leaves  grown  later,  however,  may  be  entirely  normal. 

2 These  data  were  calculated  for  only  a portion  of  the  samples  of  mottled  leaves,  because  the  average 
weight  of  the  leaves  was  not  determined  for  all  the  samples. 

3 Jensen  (7)  found  that  the  yellow  spots  of  mottled  orange  leaves,  similar  to  those  discussed  here,  contain 
less  calcium  than  the  remaining  portion  of  the  leaf. 


i78 


Journal  of  Agricultural  Research 


Vol.XX,No.  3 


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Nov.  i,  1920  Composition  of  Normal  and  Mottled  Citrus  Leaves  179 


Severely  mottled  lemon  and  grapefruit  leaves  have  also  been  analyzed 
(Tables  XII  and  XIII). 

The  results  show  that  the  composition  of  mottled  lemon  and  grape- 
fruit leaves  is  similar  to  that  of  mottled  orange  leaves.  As  was  found 
from  the  analysis  of  normal  leaves,  the  composition  of  lemon  leaves 
closely  resembles  that  of  Valencia  orange  leaves,  while  the  composition 
of  grapefruit  leaves  was  found  to  be  like  that  of  Navel  leaves.  How- 
ever, the  different  varieties  and  species  do  not  vary  greatly  in  com- ' 
position. 

The  fact  that  the  composition  of  the  leaves  of  one  species  of  citrus  is 
affected  in  the  same  general  way  as  that  of  other  species  is  not  surprising, 
since  their  appearance  when  mottled  is  also  similar. 

As  is  well  known,  it  is  rare  that  all  the  leaves  on  a given  orange  tree 
are  mottled.  As  a rule,  those  growing  on  the  outer  portions  of  the  tree 
are  the  most  severely  affected,  as  sometimes,  although  not  invariably, 
is  the  case  with  the  leaves  borne  on  the  south  and  southeastern  portion 
of  the  trees.  The  leaves  of  severely  affected  trees,  however,  may  be 
mottled  throughout  the  tree.  Frequently  the  greater  portion  of  the 
leaves  borne  by  the  shoots  of  a given  growth  cycle  may  be  mottled,  while 
those  immediately  preceding  and  following  this  cycle  may  be  entirely 
normal  in  appearance.  It  is  interesting,  therefore,  to  compare  the  com- 
position of  normal  and  mottled  leaves  from  the  same  tree. 

With  this  end  in  view,  samples  of  normal-appearing  leaves  were  col- 
lected from  the  same  trees  from  which  some  of  the  previously  discussed 
samples  of  mottled  leaves  were  drawn  and  on  the  same  days.  The 
analyses  are  reported  in  Tables  XIV  and  XV. 

The  data  are  concordant  with  the  previously  reported  analyses  of 
normal  leaves  (Tables  I and  II).  The  results  suggest  that  the  leaves  of 
different  cycles  of  growth  are  mutually  independent  in  composition  and 
that  the  peculiarities  in  the  composition  of  mottled  leaves  are  not  due  to 
any  special  peculiarity  of  the  tree  upon  which  they  have  grown.  A leaf 
of  normal  appearance  borne  by  an  orange  tree  the  major  portion  of 
whose  foliage  is  severely  mottled,  as  were  some  of  these  samples,  has 
approximately  the  same  composition  as  any  other  normal  orange  leaf. 

Some  study  has  also  been  devoted  to  citrus  trees  affected  by  chlorosis1 
and  injured  by  alkali,  the  results  of  which  will  be  presented  elsewhere. 

The  composition  of  albino  and  etiolated  plants  is  of  interest  in  this 
connection.  Church  (4,  5)  analyzed  the  normally  green  and  albino  por- 
tions of  the  maple  {Acer  negundo),  holly  {Ilex  aquifolium),  ivy  {Hedera 
helix),  and  several  other  species.  He  found  that  the  albino  portions 
uniformly  contained  greater  amounts  of  water  than  the  green  portions. 
The  ash  of  the  former  contained  greater  amounts  of  potash  and  phos- 
phoric acid  and  lesser  amounts  of  lime  than  the  latter,  while  the  content 
of  iron  was  approximately  the  same. 

1 Chlorosis  of  citrus,  as  it  occurs  in  California,  is  distinguishable  from  mottle-leaf  by  a general  fading  of 
the  chlorophyl  over  the  entire  mesophyl  tissue,  while  mottle-leaf,  as  the  name  implies,  denotes  the  lack  of 
chlorophyl  in  spots  between  the  veins. 


i8o 


Journal  of  Agricultural  Research 


Vol.XX,No.  3 


Arlington Dec.  10,1917  64.83  16.09  o.  28  | 0.013  3.91  0.41  2.46  0.05  0.32  0.33  2.86  0.05 


Nov.  i,  1920 


Composition  of  Normal  and  Mottled  Citrus  Leaves 


181 


Riverside,  plot  A June  13,  1916  57-63  17-32  (°)  (a)  | 5.50  0.27  0.82  0.09  0.12  0.29  2.23  0.06 

Riverside,  plot  H do 55-71  20.23  ( a ) (a)  [ 6.83  .36  .63  - n .15  .34  2.35  .03 

Riverside,  plot  U do 58.33  18.05  (a)  (a)  I S-91  -31  - 78  .09  .14  .22  1.92  .05 


1 82 


Journal  of  Agricultural  Research 


Vol.XX/No.  3 


Palladin  ( 14 ) also  found  that  the  composition  of  the  normal  green  and 
etiolated  specimens  of  Vicia  faba , the  latter  having  been  grown  in  the 
absence  of  light,  differed  in  composition  in  the  same  general  way  as  the 
normal  and  albino  plants  reported  by  Church.  Weber  ( 16 ) studied  the 
effects  of  different  parts  of  the  spectrum  on  the  composition  of  plants 
and  found  similar  effects.  Jensen  (7)  has  recorded  similar  observations 
on  the  leaves  of  the  privet  plant,  Ligustrum  aurea. 

While  the  fundamental  cause  of  vegetable  albinism  is  not  known, 
the  fact  that  light  of  certain  wave  lengths  is  essential  to  the  formation  of 
chlorophyl  is  well  known;  but  in  mottled  citrus  leaves  the  deficiency 
of  chlorophyl  certainly  can  not  be  caused  by  an  insufficiency  of  light. 

The  fact  that  the  composition  of  albino  and  etiolated  plants  differs 
from  that  of  normal  specimens  in  the  same  general  way  as  is  the  case 
with  mottled  and  normal  citrus  leaves  shows  that  different  causes 
may  bring  about  similar  effects  in  different  species  of  plants.  This  fact 
also  suggests  at  once  that  the  composition  of  a plant  may  not  afford  a 
safe  basis  for  forming  a judgment  as  to  the  cause  of  a particular  phenom- 
enon. A satisfactory  elucidation  of  these  questions  is  not  possible  at 
present  owing,  in  part  at  least,  to  the  lack  of  definite  knowledge  con- 
cerning the  fundamental  principles  underlying  the  growth  processes  of 
plants.  The  formation  of  chlorophyl  is  undoubtedly  the  result  of  a 
number  of  interdependent  factors,  and  it  is  highly  probable  that  either 
the  absence  or  the  inhibition  of  any  one  of  these  factors  may  prevent  the 
formation  of  chlorophyl  or  ultimately  lead  to  its  decomposition. 

COMPOSITION  OF  THE  SA.P  OF  ORANGE  LEAVES 

Some  study  has  also  been  devoted  to  the  sap  of  orange  leaves.  The 
sap  was  obtained  by  first  subjecting  the  leaves  to  a temperature  a few 
degrees  centigrade  below  zero  for  a period  of  several  hours.  Im- 
mediately after  the  leaves  were  removed  from  the  freezing  chamber 
they  were  quickly  ground  to  a pulp  with  an  ordinary  meat  grinder. 
The  juice  was  then  pressed  from  the  pulp  by  the  use  of  a hand-screw 
press.  A portion  of  the  juice  was  filtered  through  folded  filter  paper, 
and  its  specific  gravity  was  determined  by  the  pycnometer.  Partial 
analysis  was  made  on  weighed  portions  of  the  juice  by  first  evaporating 
to  dryness  and  then  using  the  methods  previously  described.  Special 
investigations  were  also  made  on  unfiltered  portions  of  the  sap  as  described 
below. 

Mature  normal  leaves,  collected  from  healthy  navel  orange  trees  on 
May  29,  1918,  were  first  studied.  A sample  of  861  gm.  of  leaves  yielded 
approximately  150  cc.  of  sap.  Partial  analysis  gave  the  following  results: 


Specific 

gravity. 

Ca. 

K. 

P. 

1.  08 

Per  cent. 

I.  07 

Per  cent. 

O.  54 

Per  cent. 

O.  036 

Nov.  i,  1920 


Composition  of  Normal  and  Mottled  Citrus  Leaves  183 


These  data  show  that  the  expressed  sap  of  mature  orange  leaves  is 
comparatively  rich  in  solids,  calcium,  and  potassium,  but  the  ratio  of 
calcium  to  potassium  in  the  sap  is  widely  different  from  the  ratio  of  the 
total  amounts  of  these  elements  in  the  leaf.  (Table  II.) 

On  June  5,  1918,  three  sets  of  samples  of  Valencia  orange  leaves  were 
collected.  One  of  these  was  composed  of  normal  leaves  about  6 weeks 
of  age;  another  sample  obtained  from  the  same  trees  consisted  of  healthy 
mature  leaves;  whereas  the  third  sample  was  chosen  to  represent  severely 
mottled  leaves  of  the  previous  yearns  growth.  Each  of  the  samples  was 
divided  into  three  parts,  one  of  which  was  used  to  study  the  sap,  another 
to  determine  the  water-soluble  constituents,  and  the  third  for  total 
analysis. 

The  sap  was  pressed  out  after  freezing  as  described  above.  The  water- 
soluble  constituents  were  extracted  by  first  grinding  100  gm.  of  the  fresh 
leaves  in  a meat  grinder,  shaking  with  1,000  cc.  distilled  water  for  one  hour, 
and  filtering  through  filter  paper.  Total  acidity  was  determined  by  titra- 
tion with  N/io  sodium  hydroxid,  using  phenolphthalein  as  indicator. 
It  was  necessary  to  dilute  the  sap  considerably  because  of  its  dark  color, 
and  a high  degree  of  accuracy  is  not  claimed  for  the  results.  They  are 
rather  approximations.  The  acidity  is  expressed  for  convenience  as 
anhydrous  citric  acid.1  The  results  are  presented  in  Tables  XVI,  XVII, 
and  XVIII. 


Table  XVI. — Composition  of  Valencia  orange  leaves  at  the  age  of  6 weeks 


Specific 

gravity. 

Ash. 

Ca. 

K. 

P. 

N. 

Acid. 

Sap 

Per  cent. 
I.  065 

I.  005 

Per  cent. 

3-  17 

Per  cent. 
O.  67 
i-  57 
3-  56 

Per  cent. 

0.  72 

1.  69 
99 

Per  cent. 
O.  045 

• *3 
. 21 

Per  cent. 

Per  cent. 

Water  extract a 

I.  64 

Total  leaf  a 

i3-  23 

2-45 

a Expressed  in  terms  of  dry  matter. 


Table  XVII. — Composition  of  normal  mature  Valencia  leaves 


Specific 

gravity. 

Ash. 

Ca. 

K. 

P. 

N. 

Acid. 

Sap 

Per  cent. 
I.  097 

I.  008 

Per  cent. 
4-32 

Per  cent. 

1.  41 

2.  85 

5-  78 

Per  cent. 
O.  42 
. 64 
•94 

Per  cent. 

o-  035 
. 063 
• 13 

Per  cent. 

Per  cent. 

Water  extract  a 

I*  15 

Total  leaf  a 

I7-  56 

I.  92 

a Expressed  in  terms  of  dry  matter. 


1 The  nature  of  the  acid  constituents  of  the  leaves  has  not  been  investigated  sufficiently  to  justify  a 
definite  statement  as  to  their  identity. 


184 


Journal  of  Agricultural  Research 


Vol.XX,No.  3 


The  results  show  that  the  sap  of  Valencia  orange  leaves  at  the  age  of 
6 weeks  contains  smaller  amounts  of  dissolved  solids  and  total  ash  ma- 
terial than  mature  leaves.  The  calcium  content  increases  more  than  two- 
fold, and  the  potassium  and  phosphorus  content  decreases  in  passing  to 
maturity.  On  the  other  hand,  the  sap  of  mottled  leaves  has  a higher 
specific  gravity  and  a higher  ash  content  than  that  of  mature  normal 
leaves.  The  calcium  content,  however,  is  considerably  less,  while  the 
potassium  and  phosphorus  content  is  much  higher. 

It  is  evident  from  these  data,  therefore,  that  the  sap  of  mottled  Valen- 
cia orange  leaves  is  materially  different  from  that  of  normal  leaves, 
either  when  they  are  6 weeks  of  age  or  mature. 

The  water-soluble  constituents  were  found  to  diverge  in  the  same 
general  direction  as  the  sap.  It  is  interesting  to  note  that  a very  high 
percentage  of  the  potassium,  phosphorus,  and  calcium  of  orange  leaves 
is  soluble  in  water. 

Samples  of  fully  mature  normal  leaves  and  of  severely  mottled  leaves 
of  the  previous  year’s  growth  were  collected  from  Navel  orange  trees  of 
the  fertilizer  plots  at  Riverside  in  August,  1918.  The  sap  was  expressed 
and  used  for  more  complete  chemical  study.  (Tables  XIX  and  XX.) 


Table  XVIII. — Composition  of  mottled  Valencia  leaves 


Specific 

gravity. 

Ash. 

Ca. 

K. 

P. 

N. 

Acid. 

Sap 

Per  cent. 
I.  Il8 

I.  009 

Per  cent. 
4-  85 

Per  cent. 

I-  !3 

2.  81? 
4-  OS 

Per  cent. 

0.  91 

1.  64 

I.  98 

Per  cent. 
O.  Ill 

. 180 
•243 

Per  cent. 

Per  cent. 

Water  extract  a.  . . 

2.75 

Total  leaf  a 

15.  06 

3.  OO 

« Expressed  in  terms  of  dry  matter. 


The  results  are  fairly  concordant  with  those  reported  above  for  Valencia 
leaves.  It  is  again  shown  that  the  composition  of  the  sap  of  mottled 
orange  leaves  differs  widely  from  that  of  normal  leaves.  The  data  also 
show  that  the  ash  of  the  sap  of  each  sample  contained  considerably 
smaller  percentages  of  calcium  and  higher  percentages  of  iron  than 
those  reported  above  for  the  ash  of  the  leaf  as  a whole,  while  the  per- 
centages of  the  other  constituents  are  not  materially  different  from 
those  of  the  entire  leaf.  The  calcium  content  of  the  sap  of  Navel 
orange  leaves  appears  to  be  lower  than  that  of  Valencia  leaves.  (Com- 
pare Tables  XVII  and  XX.) 

Upon  studying  the  preceding  data,  it  seems  difficult  to  escape  the  con- 
clusion that  there  must  be  some  important  physiological  significance 
attached  to  the  fact  that  the  sap  of  mottled  orange  leaves  contains  only 
about  one-half  as  much  calcium  and  approximately  twice  as  much 
potassium  and  nitrogen  and  three  times  as  much  phosphorus  as  normal 
leaves. 


Table  XIX. — Composition  of  the  sap  of  mature  normal  and  mottled  Navel  orange  leaves 


Nov.  i,  1920 


Composition  of  Normal  and  Mottled  Citrus  Leaves  185 


i86 


Journal  of  Agricultural  Research 


Vol.XX,No.  3 


The  hydrogen-ion  concentration  of  the  sap  was  also  determined  by  the 
use  of  the  hydrogen  electrode.  Mature  normal-leaf  sap  was  found  to 
give  a PH  value  of  5.816  and  mottled-leaf  sap  a value  of  5.647,  which 
implies  hydrogen-ion  concentrations  of  0.153  X 10 -5  and  0.226  X 10  ~5, 
respectively.  These  determinations  are  probably  within  the  range  of 
variation  of  different  samples  of  the  same  leaves. 

After  the  determination  of  the  hydrogen-ion  concentration,  total  acidity 
was  determined  by  titration,  using  the  hydrogen  electrode  to  determine 
the  end  point.  It  was  found  that  10  cc.  of  the  normal  sap  required  3 cc. 
N/10  alkali  and  the  mottled-leaf  sap  7.05  cc.  In  other  words,  the  actual 
acidity  (hydrogen-ion  concentration)  of  mottled-leaf  sap  is  approximately 
the  same  as  that  of  normal  leaves,  but  the  latter  sap  is  more  nearly  sat- 
urated with  base.  It  is  probable  that  in  each  case  the  ionization  of  the 
acids  is  held  at  approximately  the  same  level  by  the  buffers  present. 

Samples  of  normal  Navel  orange  leaves  approximately  one  wreek  of 
age,  fully  mature  .leaves,  and  severely  mottled  leaves  of  the  previous 
year’s  growth  were  collected  in  April,  1919.  The  sap  was  expressed, 
and  the  hydrogen-ion  concentration  and  total  acidity  were  determined 
by  the  hydrogen  electrode.  Freezing-point  depressions  were  also  deter- 
mined in  portions  of  the  unfiltered  sap.  The  acidity  is  expressed  in  cubic 
centimeters  of  N/10  sodium  hydroxid  required  to  neutralize  10  cc.  of  the 
sap. 

Table  XXI. — Acidity  and  freezing-point  depression  of  orange-leaf  sap 


Condition  of  leaves. 

Ph. 

Hydrogen-ion  con- 
centration. 

Total  acid- 
ity. 

Freezing- 
point  de- 
pression. 

Normal,  1 week  old 

6.  069 

O.  852  X IO-6 

O 

00 

v>  .J 

O 

°C. 

1.258 

Normal,  mature 

5.  664 

.217  X IO"5 

3.  80 

1.588 

Mottled 

5-  647 

. 226  X 10  5 

7.  OO 

i-  734 

Mottled 

5-  63° 

.235  X io“5 

8.  25 

These  data  show  that  the  actual  acidity  (hydrogen-ion  concentration) 
of  mature  orange-leaf  sap  is  approximately  two  and  one-half  times  as 
great  as  that  of  leaves  at  the  age  of  1 week;  but  again  it  is  shown  that 
the  acidity  of  mottled  leaves  is  approximately  the  same  as  that  of  nor- 
mal leaves.  The  capacity  to  neutralize  base — that  is,  total  acidity — 
however,  was  fully  twice  as  great  in  mature  leaves  as  in  those  1 week  of 
age,  while  the  mottled-leaf  sap  neutralized  about  twice  as  much  base 
as  the  normal  mature  leaf  sap. 

The  freezing-point  depressions  show  that  while  the  normal  mature- 
leaf  sap  is  more  concentrated  than  that  of  young  leaves  the  sap  of  mot- 
tled leaves  is  more  concentrated  than  either. 

The  results  of  the  preceding  investigation  on  the  sap  of  orange  leaves 
are  very  suggestive.  They  are  in  harmony  with  the  preceding  ash 


Nov.  i,  1920  Composition  of  Normal  and  Mottled  Citrus  Leaves  187 

analyses  in  that  they  indicate  that  the  composition  changes  materially 
as  growth  proceeds  and  that  the  composition  of  mottled  leaves  differs 
from  that  of  normal  leaves. 

It  is  interesting  to  note  that  the  total  water  content  of  mottled  and 
normal  mature  leaves  is  roughly  correlated  with  the  concentration  of 
the  sap,  but  this  correlation  does  not  hold  when  immature  leaves  are 
compared  with  mature  leaves. 

GENERAL  DISCUSSION 

It  has  been  shown  that  the  composition  of  orange  leaves  changes 
rapidly  as  growth  takes  place.  The  relationships  between  the  several 
constituents  drawn  from  the  soil  undergo  important  alterations.  The 
percentages  of  potassium  and  phosphorus,  when  expressed  on  the  basis 
of  either  the  ash  or  the  dry  matter,  decline  rapidly  during  the  early  part 
of  the  growth  cycle  and  continue  to  decline,  although  at  reduced  rates, 
during  the  latter  part  of  the  growth  period.  The  percentages  of  nitro- 
gen in  the  dry  matter  also  decrease  as  growth  proceeds.  The  percent- 
age of  calcium,  on  the  other  hand,  increases  rapidly  at  first,  and  later 
more  slowly.  The  concentration  of  iron  is  greatest  in  very  young  leaves, 
but  later  its  concentration  decreases  slowly,  while  no  very  pronounced 
changes  take  place  in  the  percentages  of  the  other  constituents.  The 
concentration  of  the  different  constituents  probably  remains  practically 
constant  throughout  the  period  of  normal  maturity. 

As  the  leaves  approach  senility  just  preceding  the  time  of  normal 
dropping,  notable  amounts  of  potassium  and  nitrogen  are  translocated 
back  into  the  stem  or  other  portions  of  the  tree.  A part  of  the  phos- 
phorus also  appears  to  leave  the  leaf  sometime  preceding  the  period  of 
normal  maturity.  In  contrast  to  certain  cereals,  the  absolute  content 
of  magnesium  does  not  decrease  as  maturity  approaches. 

It  has  been  shown  that  a given  orange  leaf  normally  contains  the 
maximum  amounts  of  potassium,  phosphorus,  and  nitrogen  by  the  time 
it  is  approximately  6 weeks  of  age.  I‘t  is  interesting  that  the  leaf  also 
reaches  its  maximum  size  about  the  same  time.  On  the  other  hand,  the 
absolute  content  of  calcium  continues  to  increase  until  full  maturity  is 
reached. 

Mature  orange  leaves  are  extremely  rich  in  certain  nutrients.  The  con- 
tent of  carbonated  ash  ranges  from  14  to  18  per  cent  of  the  dry  matter,  and 
the  nitrogen  content  is  usually  above  2 per  cent.  The  most  pronounced 
characteristic  of  the  orange  leaf,  however,  is  found  in  its  highly  calcareous 
nature.  When  the  leaf  is  mature,  the  dry  matter  contains  from  5 to  6 
per  cent  of  calcium. 

Lemon  and  grapefruit  leaves  are  similar  in  composition  to  orange  leaves. 

The  composition  of  mottled  citrus  leaves  is  widely  different  from  that 
of  normal  leaves.  The  difference  lies  mainly  in  the  smaller  calcium 
content,  on  the  one  hand,  and  the  greater  content  of  potassium  and 


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Vol.  XX,  No.  3 


phosphorus,  on  the  other.  Usually  the  nitrogen  content  of  mottled 
leaves  is  also  abnormally  high.  The  composition  of  mottled  orange 
leaves  resembles  that  of  immature  leaves,  although  the  percentages  of 
ash  and  nitrogen  in  the  former  are  materially  greater  than  in  the  latter. 

It  has  been  shown  that  the  absolute  amounts  of  potassium  and  phos- 
phorus contained  in  mottled  orange  leaves  are  fully  as  great  as  ordi- 
narily occur  in  normal  leaves  that  are  two  or  three  times  as  large,  while 
the  calcium  content  is  not  more  than  one-third  that  occurring  in  average 
normal  leaves. 

The  sap  of  normal  orange  leaves  becomes  increasingly  concentrated  and 
acidic  as  growth  proceeds.  When  mature  it  is  especially  rich  in  calcium 
and  contains  fully  twice  as  much  of  this  element  as  of  potassium. 

The  abnormalities  of  mottled  leaves  noted  above  also  occur  in  the  sap 
and  among  the  water-soluble  constituents.  The  sap  of  mottled  leaves 
contains  subnormal  amounts  of  calcium  and  fully  twice  as  high  concentra- 
tions of  potassium  and  phosphorus  as  mature  normal  leaves.  The 
hydrogen-ion  concentration  of  mottled  leaves  is  not  materially  different 
from  that  of  normal  leaves,  but  the  sap  is  less  nearly  saturated  with  base. 
In  other  words,  abnormally  large  amounts  of  unionized  acids  occur  in 
mottled-leaf  sap. 

Limited  study  of  portions  of  citrus  trees  other  than  the  leaves  in- 
dicates that  the  composition  of  the  leaf  spurs  of  severely  mottled  trees 
varies  from  the  normal  in  much  the  same  way  as  the  leaves.  The  compo- 
sition of  the  older  wood,  however,  is  more  nearly  normal.  On  the  other 
hand,  both  the  large  roots  and  small  rootlets  of  severely  mottled  trees 
appear  to  contain  considerably  less  potassium  and  phosphorus  than  nor- 
mal roots,  while  the  calcium  content  is  approximately  normal. 

Should  more  extended  study  confirm  these  latter  observations*  it 
would  seem  that  the  excessive  proportions  of  potassium  and  phosphorus 
occurring  in  mottled  leaves  may  have  been  drawn,  in  part  at  least,  from 
the  supply  normally  stored  in  the  roots. 

The  results  of  these  investigations  suggest  that  mottled  citrus  trees 
are  deficient  in  calcium,  but  the  cause  of  the  subnormal  content  of 
calcium  can  not  be  definitely  stated. 

While  we  recognize  that  growing  plants  have  the  power,  through 
selective  absorption,  of  regulating  their  composition  to  a marked  degree, 
and  that  a given  variation  in  the  composition  of  a plant  does  not  neces- 
sarily reflect  a corresponding  deficiency  in  the  nutrient  medium,  the  above 
data  suggest  that  the  abnormalities  in  the  composition  of  different  parts 
of  mottled  citrus  trees  may  be  due,  in  part  at  least,  to  the  inability  of  the 
tree  to  satisfy  its  normal  calcium  requirements  at  critical  periods. 

It  is  well  known  that  manure  and  other  forms  of  decaying  organic 
matter  exert  an  ameliorating  effect  on  mottle-leaf.  It  is  interesting  in 
this  connection  that  the  concentration  of  soluble  calcium  in  the  soil 


Nov.  x,  1920  Composition  of  Normal  and  Mottled  Citrus  Leaves  189 


becomes  materially  increased  as  a result  of  the  decomposition  of  such 
materials  ( 8 ).  On  the  other  hand,  the  occurrence  of  heavily  compacted 
layers  of  soil  (plowsole)  around  the  roots,  especially  when  present  im- 
mediately below  the  depth  of  cultivation,  and  of  soils  of  low  organic 
content  (3)  and  low  natural  solubility  afford  conditions  that  are  con- 
ducive to  mottle-leaf.  Where  such  conditions  occur,  it  is  possible  that 
the  supplies  of  those  nutrients  which  are  normally  absorbed  at  relatively 
high  rates  may  become  inadequate.  The  nature  and  extent  of  the  root 
system  of  citrus  trees  must  also  be  considered  in  this  connection.  It  is 
interesting  that  the  absorbing  roots  of  citrus  trees  are  not  provided  with 
the  usual  root  hairs.  Consequently,  they  may  possess  less  absorbing 
surface  than  is  afforded  by  other  plants  that  normally  absorb  relatively 
large  amounts  of  nutrients.  These  and  other  related  questions  will  be 
more  fully  discussed  elsewhere. 

The  fact  that  mottle-leaf  sometimes  appears  on  trees  that  have  been 
injured  by  alkali  suggests  the  possibility  that  alterations  in  permeability 
occasioned  by  the  presence  of  excessive  concentrations  of  salts,  or  pos- 
sibly toxic  substances  of  other  kinds  in  the  soil  moisture,  may  prevent 
the  roots  from  taking  up  normal  amounts  of  calcium.1 

If  we  may  judge  from  the  composition  of  normal  leaves,  the  calcium 
requirements  during  the  period  when  mottle-leaf  develops  most  pro- 
nouncedly are  extremely  heavy.  The  leaves  at  that  stage  normally  absorb 
calcium  at  a high  rate. 

Just  why  subnormal  concentrations  of  calcium  accompanied  by  super- 
normal concentrations  of  potassium  and  phosphorus  in  the  leaves  should 
afford  conditions  that  tend  to  limit  chlorophyl  production  is  not  known, 
if  indeed  further  investigations  prove  that  such  is  the  case.  There  may, 
of  course,  be  no  causal  relationship  between  these  facts,  but  rather  each 
may  be  the  result  of  causes  not  yet  suggested. 

It  is  recognized  that  calcium  is  not  a normal  constituent  of  chlorophyl. 
In  addition,  while  iron  is  essential  to  the  formation  of  chlorophyl  yet 
does  not  enter  into  its  final  composition,  we  are  not  aw^are  that  a similar 
relationship  exists  between  calcium  and  chlorophyl  formation.  Conse- 
quently, even  though  further  study  should  prove  that  mottle-leaf  can  be 
produced  as  a result  of  an  inadequate  supply  of  available  calcium,  it  is 
probable  that  the  lack  of  chlorophyl  and  its  disappearance  from  the 
localized  areas  of  the  leaves  would  be  found  to  be  indirect  rather  than 
direct  effects  of  a shortage  of  calcium.  In  any  event,  whether  the 
shortage  of  calcium  or  some  other  factor  conditions  the  deficiency  of 
chlorophyl,  photosynthesis  is  doubtless  reduced  by  the  lack  of  chlorophyl. 

With  an  adequate  supply  of  nitrogen,  phosphorus,  and  potassium  pres- 
ent in  the  soil  moisture,  osmosis  might  bring  about  the  absorption  of 

1 As  is  well  known,  the  occurrence  of  mottle-leaf  is  sometimes  correlated  with  the  species  of  root  stock, 
but  this  phase  of  the  subject  has  not  been  systematically  investigated  in  California.  Mr.  H.  Atherton 
Lee  has  called  the  writer’s  attention  to  his  studies  on  this  phase  of  mottle-leaf  in  the  Philippine  Islands. 


190 


Journal  of  Agricultural  Research 


Vol.XX,  No.  3 


greater  or  lesser  amounts  of  them,  despite  the  deficiency  of  chlorophvl 
in  the  leaves;  but  the  reasons  why  excessive  amounts  of  these  elements 
accumulate  in  mottled  citrus  leaves  are  not  clear.  It  seems  probable 
that  some  physico-chemical  principle  not  elucidated  by  the  preceding 
data  must  be  fundamentally  involved. 

Before  any  explanation  of  mottle-leaf  can  be  safely  accepted,  it  is 
necessary  to  show  that  the  disease  can  be  produced  experimentally,  and 
that  too  under  conditions  admitting  of  scientific  analysis.  Additional 
studies  already  projected  may  throw  further  light  on  this  subject. 

Whatever  may  ultimately  be  found  to  be  the  primary  cause  of  mottle- 
leaf,  the  preceding  investigations  strongly  suggest  that  the  leaves  are 
not  suffering  from  inadequate  supplies  of  potassium,  phosphorus,  or 
nitrogen.  We  have  also  found  little,  if  any,  indication  of  a deficiency  of 
iron. 

literature  cited 

(1)  Alino. 

1901.  THE  cultivation  of  oranges.  In  Jour.  Roy.  Hort.  Soc.  [London],  v, 
25.  Pt-  3>  P-  34I-352- 

(2)  Blair,  A.  W. 

[1910.]  report  of  chemist.  In  Fla.  Agr.  Exp.  Sta.  Rpt.  [i909]/io,  p.  xxv- 
xxxiv. 

(3)  Briggs,  Lyman  J.,  Jensen,  C.  A.,  and  McLane,  J.  W. 

1916.  mottle-leaf  of  citrus  trees  in  relation  to  soil  conditions.  In 

Jour.  Agr.  Research,  v.  6,  no.  19,  p.  721-740,  4 fig.,  pi.  H,  96-97. 

(4)  Church,  A.  H. 

1879.  a chemical  study  of  vegetable  albinism.  In  Jour.  Chem.  Soc. 
[London],  v.  35,  p.  33-41. 

(5)  — 

1886.  A CHEMICAL  STUDY  OF  VEGETABLE  ALBINISM.  PART  HI.  EXPERIMENTS 
with  quErcus  rubra.  In  Jour.  Chem.  Soc.  [LondonJ,  v.  49,  p. 
839-843. 

(6)  Ensign,  M.  R. 

1919.  VENATION  AND  SENESCENCE  OF  POLYEMBRYONIC  CITRUS  PLANTS.  In 
Amer.  Jour.  Bot.,  v.  6,  no.  8,  p.  311-329,  6 fig.  Bibliography,  p.  329. 

(7)  Jensen,  C.  A. 

1917.  COMPOSITION  OF  CITRUS  LEAVES  AT  VARIOUS  STAGES  OF  MOTTLING.  In 

Jour.  Agr.  Research,  v.  9,  no.  6,  p.  157-166.  Literature  cited,  p.  166. 

(8)  — 

1917.  EFFECT  OF  DECOMPOSING  ORGANIC  MATTER  ON  THE  SOLUBILITY  OF  CER- 
TAIN inorganic  constituents  of  the  soil.  In  Jour.  Agr.  Research, 
v.  9,  no:  8,  p.  253-268. 

(9)  Jones,  W.  J.,  Jr.,  and  Huston,  H.  A. 

1914.  COMPOSITION  OF  MAIZE  AT  VARIOUS  STAGES  OF  ITS  GROWTH.  Ind.  Agr, 
Exp.  Sta.  Bui.  175,  p.  599-629,  10  fig.,  i fold.  pi.  (col.). 

(10)  Kelley,  W.  P.,  and  Thompson,  Alice  R. 

1910.  a study  of  the  composition  of  the  rice  plant.  Hawaii  Agr.  Exp. 
Sta.  Bui.  21,  51  p. 

(11)  McBeth,  I.  G. 

1917.  RELATION  OF  THE  TRANSFORMATION  AND  DISTRIBUTION  OF  SOIL  NITRO- 
GEN To  the  nutrition  of  citrus  plants.  In  Jour.  Agr.  Research, 
v.  9,  no.  7,  p.  183-252,  19  fig.  Literature  cited,  p.  251-252. 


Nov.  i,  1930  Composition  of  Normal  and  Mottled  Citrus  Leaves 


191 


(12)  Muller,  John. 

1909.  yellowing  of  citrus  Trees.  In  Agr.  Jour.  Cape  Good  Hope,  v.  34, 
no.  2,  p.  i49-i57>  2 %• 

(13)  Olivieri,  V.,  and  GuerriEri,  F. 

1895.  ricerche  suc-li  agrumi.  In  Staz.  Sper.  Agr.  Ital.,  v.  28,  fasc.  5,  p. 
287-301. 

(14)  Palladin,  W. 

1892.  aschengehalt  dEr  ETiolirten  blatter.  In  Ber.  Deut.  Bot.  Gesell., 
Bd.  10,  p.  179-183. 

(15)  RownEy,  Thomas  H.,  and  How,  Henry. 

1848.  ANALYSIS  OF  THE  ASHES  OF  THE  ORANGE-TREE  (CITRUS  AURANTIUM). 
In  Mem.  and  Proc.  Chem.  Soc. 'London,  v.  3 (1845/48),  p.  370-377. 

(16)  Weber,  Rudolf. 

1875.  UEBER  DEN  EINFLUSS  FARBIGEN  LICHTES  AUF  DIE  ASSIMILATION  UND 
DIE  DAMIT  ZUSAMMENHANGENDE  VERMEHRUNG  DER  ASCHENBESTAND- 

TheilE  in  ErbsEn-keimlingen.  In  Landw.  Vers.  Stat.,  Bd.  18, 
p.  18-48. 


